The goal of this research project is to gain an understanding of the effects of cryptochidism on Leydig cell function. Using mature (60-90 day) rats that are surgically rendered bi- or unilaterally cryptorchid, these studies are designed to accomplish the following objectives: 1) Isolate and purify Leydig cells utilizing the cryptorchid rat as an animal model. Cryptorchidism results in a degeneration of the germinal epithelium and consequently an in situ enrichment of Leydig cell concentration. Through modifications of the standard isolation/purification procedures, Leydig cells will be prepared and accurately quantified from each experimental group. 2) Determine the influence of bi- and unilateral cryptorchidism on the function of Leydig cells in terms of hCG-binding and steroidogenic capacity. Binding of 125I-hCG by purified Leydig cells from each group will be measured in an attempt to assess cryptorchid-induced changes in gonadotropin binding capacity (receptors). Additional studies will determine the steroidogenic capacity of purified Leydig cells by measuring hCG-stimulated testosterone in vitro. Data analysis will determine testosterone production per ng hCG binding per 10 to the 6 Leydig cells. 3) Investigate the effects of estradiol and the dynamics of estradiol-receptor interactions in Leydig cells from cryptorchid testes. The influence of estrogens administered in vivo or added in vitro on Leydig cell androgen production will be examined. Additional studies will examine the influence of cryptorchidism on the estrogen receptor. The process of receptor translocation from cyptoplasm to nucleus will be investigated using purified Leydig cells from the cryptorchid animal. These studies will provide insight into the role of estrogens in regulating Leydig cell activity during cryptorchidism. These studies will contribute to our understanding of testicular endocrine function and will facilitate the treatment of testicular endocrinopathies such as cryptorchidism.